The present invention relates generally to computed tomography and more particularly to performing high speed x-ray computed tomography with fiber waveguides.
In computed tomography, an x-ray source projects a fan-shaped beam at an object being imaged, such as a medical patient or an engineered part. The intensity of the transmitted radiation is dependent upon the attenuation of the x-ray beam by the object. The x-ray beam passes through the object and impinges upon an array of radiation detectors. Each detector in the array produces a separate electrical signal that is a measurement of the beam attenuation. The attenuation measurements from all of the detectors are acquired separately to produce a transmission profile.
In a conventional x-ray computed tomography (CT) system, the x-ray source and detector array are rotated on a gantry within the imaging plane and around the object, so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements from the detector array at a given angle is referred to as a "view". A "scan" of the object represents a set of views made at different angular orientations during one revolution of the x-ray source and the detector. The data for a given scan is stored in memory as a two-dimensional array with storage locations along one axis of the array representing the data from each radiation detector and the storage locations along the other axis containing data for the different views. The scan data is then processed to construct an image that corresponds to a two-dimensional slice taken through the object. A series of two-dimensional slices are used to form a three-dimensional scan.
A problem with the conventional CT system is that its use in medical and industrial applications is limited by the speed of the x-ray source and the gantry that is used to rotate the source around the object being imaged. In particular, for medical applications, the gantry rotates the x-ray source around the object at a scan cycle ranging from about 0.5 seconds to about 1.0 seconds. The x-ray source uses x-ray tube inserts that have rotating target velocities ranging between 2000RPM and 9000 RPM. The dynamic forces resulting from moving a rotating target within a tube limit the gantry rotational speed. In addition to constraining scanning speed, the dynamic forces decrease the life of the x-ray tube and increase the amount of service needed to maintain the CT system. Typically, these x-ray tubes are limited to about 100,000 to about 200,000 scans. As a result of the decreased x-ray tube life and increased service, the overall reliability of the CT system for medical applications is jeopardized over time. In industrial applications, the conventional CT system has its limitations in viewing certain rotating components under load and for nondestructive testing of new designs. Viewing a component's internal mechanical integrity while under load is useful for design verification and optimization, quality assurance, and preventative maintenance. With the conventional CT system, incipient flaws and structural integrity are difficult to identify. Accordingly, there is a need for a faster, mechanically simpler, and more reliable CT system that can be used for medical and industrial applications.